The present invention relates to acoustic actuators suitable for air-acoustic and hydrodynamic applications. The invention particularly relates to acoustic actuator panels based on piezoelectric or electrostrictive ceramic arrays similar to those used as the ceramic component of a 2--2 or 1-3 ceramic/polymer composite transducer, described below, and to methods for fabricating such actuator panels.
Piezoelectric and electrostrictive ceramic/polymer composite transducer materials have been identified as having significant potential for improving the performance of many acoustic systems. Two of the most important composite configurations are those exhibiting the so-called 1-3 and 2--2 connectivity described in detail in U.S. Pat. No. 5,340,510, to Leslie J. Bowen, one of the inventors of the present application. (U.S. Pat. No. 5,340,510 is incorporated herein by reference.) The 1-3 composite is a one-dimensionally connected piezoelectric or electrostrictive ceramic phase, e.g., lead zirconate titanate (PZT) fibers, rods, or posts contained within a three-dimensionally connected polymer phase. The 2--2 composite is made up of two-dimensionally connected ceramic, e.g., PZT strips separated by two-dimensionally connected parallel polymer strips.
Specific potential applications for such acoustic systems include: undersea imaging, inspection, and surveying; acoustic signature control; acoustic noise and structural vibration suppression; medical diagnostic imaging; and industrial process control and nondestructive evaluation.
The efficient production of the composite transducers described in U.S. Pat. No. 5,340,510 and their performance advantages in hydrostatic transducer applications have been demonstrated. However, the applications to which these transducers are suited are limited by the element displacement available using the specific configurations described. Higher displacements will be required to generate useful, e.g., acoustic pressure levels (about 100dB) at low frequencies (e.g., about 100 Hz) in air and other low acoustic impedance media.
Tubular elements used in 1-3 composite arrays have proven beneficial in hydrophone applications (Zhang et al., J. Mat. Sci. 28, pp. 3962-3968 (1993), incorporated herein by reference), since they exhibit a high displacement at very low voltages. However, the cost of the tubular ceramic element composites known in the prior art is prohibitive, and displacement obtainable with arrays of such prior art tubular elements is still insufficient for air-acoustic applications.
In another context, transducers are known which exploit the flextensional properties of a flexible shell surrounding a piezoelectric driver element. Such flextensional transducers are defined in accordance with the shape of the shell, as described in the following papers, both incorporated herein by reference: D. Boucher, "New Solutions for Low Frequency Sonar Projectors" and E. F. Rynne, "Innovative Approaches for Generating High Power, Low Frequency Sound", both presented at The 3d International Workshop, Transducers for Sonics and Ultrasonics at Orlando, Fla., May 6-8, 1992 and published in its Proceedings, pp. 25 and 38, respectively. However, the displacement achievable with these flextensional transducers is too small and the transducers are too massive and stiff for many applications. Further, a thin, planar acoustic actuator is not achievable with such designs.
Accordingly, it is an object of the present invention to provide a flextensional cover plate for redirecting the vibrational displacement of terminal ends of at least one pair of piezoelectric or electrostrictive ceramic bender elements vibrating toward and away from each other.
It is another object of this invention to provide a method for redirecting such terminal end vibrational displacement, and for amplifying the displacement by flextensional means.
It is yet another object of the present invention to provide an acoustic actuator panel configuration exhibiting a sufficiently high element displacement for air-acoustic as well as hydrodynamic applications.
Still other objects of this invention provide methods for fabricating such actuator panels and flextensional cover plates.